-LRB- CNN -RRB- -- A wildfire continued its rampage through the San Bernardino National Forest in Southern California on Monday , but the U.S. Forest Service said fire crews were gaining ground .

The Sheep Fire in Southern California has burned thousands of acres and left this bus a charred ruin .

`` Firefighters have made very good progress against the Sheep Fire . It 's currently at approximately 7,500 acres with 20 percent containment , '' U.S. Forest Service spokeswoman Robin Prince said Monday .

The fire , which was reported Saturday afternoon in the Lytle Creek area , quickly grew to 3,500 acres by early Sunday and forced about 4,000 people in the community of Wrightwood from their homes .

`` People are going to have to hold off on getting back to their homes until we get a little better containment lines on the fire , but things are looking really good , '' according to Prince .

More than 1,200 firefighters were battling the blaze , and numerous firefighting aircraft have dropped water and retardant on the wildfire . Back fires have been set to protect homes at the eastern edge of Wrightwood , authorities said .

The weather was cooperating Monday , unlike over the weekend when a high-wind warning remained in effect and gusty winds helped fan the flames .

`` There 's very little smoke . There 's a few flare ups here and there , but if the winds pick up , we could still have some problems . So that 's why we 're holding off on letting people go back into the mandatory evacuated area , '' said Prince .

California Gov. Arnold Schwarzenegger declared a state of emergency in San Bernardino County on Sunday so the state can mobilize agencies and equipment to help fight the fire .

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Sheep Fire is about 7,500 acres with 20 percent containment , Forest Service says

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About 4,000 people in San Bernardino County forced from their homes

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Despite more cooperative weather , people not let back into homes yet